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Determination of urea in milk is inevitable in the dairy industry for the quality control processes. A simple and cost-effective method was developed to determine the concentration of urea in milk by silver nanoparticles (uncapped and citrate capped) and ultraviolet–visible (UV–Vis) spectroscopy. The developed nanoparticles were characterized by UV–Vis, scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy and a colour change was noted from yellow to blue upon nanoparticles interaction with urea. A predictive model was developed using the spectral data from the analyzed samples. The developed model was able to measure urea concentration (between 6 mg/dL to 90 mg/dL) in milk with the coefficient of determination (R2) more than0.90 and was validated through para -dimethylaminobenzaldehyde (DMAB) method suggested by the Food Safety and Standards Authority of India (FSSAI). The average accuracy and sample percent relative standard deviation (% RSD) obtained through the developed method + model ranged from 62.67 to 121.85% and 0.11–1.21%. The regression model for uncapped nanoparticles was found to be best-fitted (having R2 = 0.92, average accuracy 103.75 ± 8.69%), with higher closeness to the values obtained for urea by FSSAI-DMAB method. This proposed study proves to be useful for the qualitative and quantitative determination of urea in milk by small businesses in the dairy industry. • Detection of urea in milk through silver nanoparticles based UV-VIS spectroscopy. • Spectral data based development of predictive model for urea determination in milk. • The method is simple, cost-effective and beneficial for quality control of milk. [ABSTRACT FROM AUTHOR]

The explosive growth in nanomaterial use will bring about their increased release into terrestrial ecosystems. Metal engineered nanomaterials (ENMs) that gain entry into these environments may alter the composition and activities of resident natural bacterial communities. To assess changes in community level physiological profiles (CLPP) of microbial communities in soils exposed to metal ENMs, Biolog EcoPlates were used in this exploratory comparative study. The CLPP is a rapid screening technique to characterise functional differences among heterotrophic microbial communities based on variable substrate utilization. The impacts of three metal ENMs, silver, titanium dioxide and zinc oxide, on bacterial communities were investigated using three soil types from Maharashtra, India. Metabolic diversity of bacterial communities was impacted in the soils in presence of silver and zinc oxide, but not in presence of titanium dioxide nanoparticles. Diversity indices, viz., Shannon's index, Evenness index and Simpson's index also showed significant differences in the presence of silver and zinc oxide nanoparticles. Principal component analysis revealed changes in metabolic profiles in the presence of silver nanoparticles. This study also shows that testing ecotoxicity of nanoparticles using readily culturable bacteria is a practical approach. • Metabolic diversity of bacterial communities impacted in soils in presence of silver and zinc oxide nanoparticles. • No significant shifts in metabolic patterns of soil bacteria on exposure to titanium dioxide nanoparticles. • Testing ecotoxicity of nanoparticles usng readily culturable bacteria is a viable approach. [ABSTRACT FROM AUTHOR]